Anyone that can help please on radical functions?

The algebraic expression: I am not sure how to type this on the computer but in the parenthesis is the square root of t+h - square root of t over h

15.92(square root of t + h - square root of t over h)

models the average rate of change in the percentage of households online from t years after 1997 to t + h years after 1997. Use the expression to solve this problem...

Let t=4 and h=2. Evaluate the expression to find the average rate of change in percentage of households online from 2001-2003 that is, between 4 years and 4 + 2, or 6 years after 1997.